1. Field of the Invention
The present invention relates to an inductor and a method of producing such an inductor, and more particularly, the present invention relates to an inductor having a conductor (internal conductor) functioning as an inductance element that is located within a magnetic material produced by kneading a magnetic powder and a resin, and a method of producing the inductor.
2. Description of the Related Art
As shown in FIG. 7, a surface-mount inductor including a magnetic material compact body 53 that is produced by molding a magnetic material 51 obtained by kneading a magnetic powder and a resin into a mold in which a coil (internal conductor) 52 functioning as an inductance element is buried in the magnetic material 51, with both ends 52a and 52b of the coil 52 exposed at both end surfaces of the magnetic material compact body 53, and a pair of external electrodes 54a and 54b provided at both end surfaces of the magnetic material compact body 53.
This inductor can be produced by molding the magnetic material 51 obtained by kneading a magnetic powder and a resin to produce the magnetic material compact body 53, and then providing the external electrodes 54a and 54b on the magnetic material compact body 53. Thus, the step of firing the inductor at high temperature is not necessary, which is required for conventional ceramic inductors including magnetic ceramic material. Therefore, the manufacturing cost of producing the inductor is decreased.
However, in forming the external electrodes of the above-described inductor by a method including the steps of coating conductive paste and baking it, like in ceramic inductors, the resin that constitutes the magnetic material compact body decomposes in response to the heat applied during baking of the conductive paste. Under actual conditions, it is very difficult to apply the conventional method using conductive paste without modification.
Therefore, a conventional inductor is shown in FIG. 8, in which metal caps 55a and 55b are mounted as external electrodes to both ends of the magnetic material compact body so as to be connected to both ends of the coil 52. However, the metal caps are expensive and require the step of mounting the metal caps, thereby increasing production cost.
In other conceivable methods of forming the external electrodes using conductive paste, special conductive paste that can be baked at low temperature is used, or a resin having excellent heat resistance is used as the resin that constitutes the magnetic material compact body. However, both of these methods are problematic because they produce inductors with diminished and inferior properties, and decrease the ease and degree of freedom of the manufacturing process.
To overcome the above-described problems, preferred embodiments of the present invention provide an inductor in which external electrodes are efficiently provided without using metal caps or baking conductive paste, and which has high reliability of connection between the external electrodes and an internal conductor, and desired properties. Preferred embodiments of the present invention also provide a method of producing such a novel inductor.
A method of producing an inductor according to preferred embodiments of the present invention includes the steps of molding a magnetic material obtained by kneading a magnetic powder and a resin into a desired shape in which a conductor (internal conductor) functioning as an inductance element is buried to form a magnetic material compact body in which the internal conductor is partially exposed at a surface thereof, and plating the surface of the magnetic material compact body to form external electrodes including a metallic film electrically connected to the portions of the internal conductor which are exposed on the surface of the magnetic material compact body.
The method of producing an inductor according to preferred embodiments of the present invention includes molding the magnetic material obtained by kneading the magnetic powder and the resin into the desired shape to form the magnetic material compact body in which the internal conductor is partially exposed at a surface thereof, and plating the surface to form the external electrodes so that the external electrodes are electrically connected to the internal conductor. Thus, the method according to preferred embodiments of the present invention eliminates the necessity of a heat-treatment step for firing in the step of forming the magnetic material compact body, baking conductive paste in the step of forming the external electrodes, while avoiding decomposition or transformation of the magnetic material in the heat treatment step, thereby permitting the efficient production of an inductor having desired properties. Further, there is also no need for equipment such as a heat treatment furnace, or other similar equipment, and thermal energy used for heat treatment, thereby reducing production costs.
In preferred embodiments of the present invention, the step of molding the magnetic material into the predetermined shape to form the magnetic material compact body in which the internal conductor is partially exposed at a surface thereof is applicable not only where the magnetic material is molded to form the magnetic material compact body including the internal conductor partially exposed at the surface thereof, but also in methods including the step of exposing the internal conductor, such as where the magnetic material compact body is cut and ground to partially expose the internal conductor at the surface after the magnetic material is molded.
The method of producing an inductor according to preferred embodiments of the present invention further includes roughening portions of the surface of the magnetic material compact, on which plated metal films are formed by plating, before such plating is performed.
By performing plating after roughening the portions of the surface of the magnetic material compact body which are to be plated, the strength of adhesion of the plated metal film to the magnetic material compact body is greatly improved, thus significantly improving reliability.
The method of producing an inductor according to preferred embodiments of the present invention includes exposing both ends of the internal conductor at both end surfaces of the magnetic material compact body, roughening at least both end surfaces thereof, and plating at least portions of the roughened surfaces to form the external electrodes.
In the method including exposing both ends of the internal conductor at both end surfaces of the magnetic material compact body, roughening at least both end surfaces thereof, and then plating at least portions"" of the roughened surfaces to form the external electrodes, the external electrodes are provided on both end surfaces of the magnetic material compact body to allow the efficient production of a chip-type inductor having excellent adaptability for surface mounting, thereby increasing the effectiveness of the present invention.
In the method of producing an inductor according to preferred embodiments of the present invention, with the internal conductor including a coiled metal conductor (coil), both end surfaces of the magnetic material compact body are roughened to expose ⅓ to 1 turn of the coil so that the coil partially projects from both end surfaces of the magnetic material compact, and then at least portions of the roughened surfaces are plated to form the external electrodes.
In the method including roughening the surface to expose about ⅓ to 1 turn of the internal conductor, which includes a coiled metal conductor (coil), so that the coil partially projects from both end surfaces of the magnetic material compact, and then forming the external electrodes by plating, a sufficient area of contact between the coil and the external electrodes is ensured, thus significantly improving reliability of electrical contact between the coil and the external electrodes.
Although a coil coated with an insulating coating material is generally used as the coil, the insulating coating material of the coil can be removed by surface roughening. Furthermore, the coil is exposed so as to partially project from both end surfaces of the magnetic material compact, thereby not only increasing the area of contact with the external electrodes, but also increasing the strength of adhesion between the external electrodes and the magnetic material compact body due to the unevenness formed on the surfaces of the magnetic material compact body on which the external electrodes are provided. This further improves the reliability of connection with the external electrodes.
The reason for exposing about ⅓ to 1 turn of the coil from the end surfaces of the magnetic material compact body is that exposure of at least about ⅓ turn of the coil causes sufficient connection reliability, and exposure of more than about 1 turn of the coil causes an undesirable short circuit in the exposed coil.
In the exposed portions of the coil, the coil is preferably exposed so as to project from both end surfaces of the magnetic material compact body by about xc2xd of the diameter of a wire constituting the coil.
The method of producing an inductor according to another preferred embodiment of the present invention includes roughening a region extending from either end surface of the magnetic material compact body to a portion of the peripheral surface (a portion at either end of the peripheral surface), and then forming the external electrode by plating so that the external electrode extends from the either end surface of the magnetic material compact body to the portion of the peripheral surface thereof.
In the method including roughening the region extending from either end surface of the magnetic material compact body to the portion of the peripheral surface thereof, and then forming the external electrode by plating so that the external electrode extends from the either end surface of the magnetic material compact body to the portion of the peripheral surface thereof, for example, in mounting by reflow soldering, the mounting workability is substantially improved, and the reliability of connection (mounting) is also substantially improved.
In the method of producing an inductor according to another preferred embodiment of the present invention, the surface of the magnetic material compact body is roughened by the medium spraying method of spraying a surface roughening medium (powder and granules).
In the method of roughening the surface of the magnetic material compact body by the method of spraying the surface roughening medium (powder and granules), for example, a dry blast method (sand blast method) in which a-medium such as an alumina powder, a silica powder or other suitable material is sprayed together with air to grind the surface of the magnetic material compact, or a wet blast method in which an alumina powder, a silica powder, or other suitable material is sprayed together with a liquid such as water to grind the surface of the magnetic material compact, the surface is efficiently roughened in a short time, thus further improving the effectiveness of the present invention.
In preferred embodiments of the present invention, surface roughening can be performed by another method, for example, which includes the steps of placing a plurality of magnetic material compacts in a barrel, and stirring the compacts. In this case, however, the time required for surface roughening is increased, thereby reducing the production efficiency as compared with the above medium spraying method.
In the method of producing an inductor of according to a preferred embodiment of the present invention, the external electrodes have a multilayer structure including a plurality of plated metal films.
In various preferred embodiments of the present invention, the structure and type of the plated metal film that constitutes the external electrodes are not particularly limited, and the external electrodes may also have a single layer structure. However, in order to ensure the solderability of the external electrodes and reliability of electric connection, a multilayer structure is preferably used. For example, an Ag plated film or Ni plated film is provided as a base electrode, and a Sn plated film or solder plated film is provided on the base electrode to provide an inductor including external electrodes having both excellent reliability of electrical connection and solderability.
An inductor according to preferred embodiments of the present invention is produced by the above-described method, and includes a magnetic material compact body formed by kneading a-magnetic powder and a resin, and molding into a desired shape, a conductor (internal conductor) buried in the magnetic material compact body and functioning as an inductance element, and external electrodes provided on the surface of the magnetic material compact body and including plated metal films electrically connected to the internal conductor.
The inductor produced by the above-described inductor producing method has the above construction, exhibits high reliability of connection between the external electrodes and the internal conductor, and is efficiently produced at low cost.
Other features, elements, steps, characteristics and advantage of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.